Change Page::m_mainFrame to be a Frame.

Source/core/page/ScopedPageLoadDeferrer.cpp

Index: Source/core/page/ScopedPageLoadDeferrer.cpp
diff --git a/Source/core/page/ScopedPageLoadDeferrer.cpp b/Source/core/page/ScopedPageLoadDeferrer.cpp
index 1387aef793672fcdcf376fd39504212cb4b80322..d911587a66b732365766bfe0691b92a3f7fd0113 100644
--- a/Source/core/page/ScopedPageLoadDeferrer.cpp
+++ b/Source/core/page/ScopedPageLoadDeferrer.cpp
@@ -41,11 +41,13 @@ ScopedPageLoadDeferrer::ScopedPageLoadDeferrer(Page* exclusion)
         if (page == exclusion || page->defersLoading())
             continue;
 
-        m_deferredFrames.append(page->mainFrame());
+        if (page->mainFrame()->isLocalFrame()) {
+            m_deferredFrames.append(toLocalFrame(page->mainFrame()));
 
-        // Ensure that we notify the client if the initial empty document is accessed before
-        // showing anything modal, to prevent spoofs while the modal window or sheet is visible.
-        page->mainFrame()->loader().notifyIfInitialDocumentAccessed();
+            // Ensure that we notify the client if the initial empty document is accessed before
+            // showing anything modal, to prevent spoofs while the modal window or sheet is visible.
+            toLocalFrame(page->mainFrame())->loader().notifyIfInitialDocumentAccessed();
+        }
 
         // This code is not logically part of load deferring, but we do not want JS code executed
         // beneath modal windows or sheets, which is exactly when ScopedPageLoadDeferrer is used.